1. Technical Field
The present invention relates generally to devices for trench shoring and, more specifically, to a device that may be readily positioned and moved along a length of trench, for shoring the trench.
2. Background
Trench shoring is used to secure the sides of ditches and trenches which may be occupied by laborers during operations which may occur at the bottom of the trench, oftentimes in utility construction and maintenance. Trench shoring typically consists of two opposing panels which are held in spaced apart relationship by a plurality of struts or spreaders which may be of a fixed and interchangeable length or in the alternative adjustable in length, thereby adjusting the distance between the spaced apart panels for any given width of ditch.
Once the trench is opened by excavation, the shoring or trench box is set into the trench. Laborers may then enter the trench and work at the bottom in a far safer environment than that which would exist in an open trench. As the trenching advances, additional trench boxes may be placed along the trench or, alternatively, a trench box may be advanced along the length of the trench as it advances with the work. In this case, the box is typically lifted by the hoe or shovel which is performing the excavation and advanced along the length of the trench and then dropped or placed into the trench.
A number of disadvantages are present with this arrangement, including the fact that the trench boxes typically set at the bottom of the ditch which reduces the clearance between the lower spreaders and the work which is being performed at the bottom of the trench. Additionally, moving the trench box or advancing the box along the trench is a cumbersome and time consuming operation.
A number of solutions have been suggested to address these and other disadvantages. West Jr., U.S. Pat. No. 3,788,086, discloses a trench barrier having a horizontal frame carriage with wheels mounted on the ends of the frame carriage. The West carriage has suspended from it a pair of spaced apart shield members which may be held in spaced apart relation by jacks extending between the shield members. West also discloses vertically disclosed cooperating telescoping struts which are carried by the carriage for adjusting the relative vertical position of the shield members, and allows for varying the height at which the shield members are suspended in the trench. However, as shown in the West disclosure, the wall members extend well past the ends of the frame carriage and the axles, thereby restricting vertical movement of the wall members to a height determined by the elevation of the frame carriage and the axles.
Arnold, U.S. Pat. No. 4,874,271, discloses a trench shoring machine having a main frame having a pair of substantially vertical guide members carried by the main frame, a pair of transversely extending carrier bars engage the pair of vertical guide members, and opposed shoring plates supported from the carrier bars which are moveable along the length of the carrier bars. Arnold further discloses a pair of shoring plates, including a top plate and a lower plate, which are movable between relatively upper and lower positions with respect to the main frame, together with means for moving the lower plate between an upper and lower position.
The Arnold device allows the shoring plates to be raised above the elevation of the axles, but accomplishes this through a configuration wherein the main frame is suspended substantially above the axles through the use of a triangular carrier frame located at each wheel. This configuration results in placement of the substantial weight of the main frame well above the axles. This configuration results in a raised center of gravity for the apparatus. During operations, which typically occur along an open trench having excavation tailings piled along either side of the trench, the heightened center of gravity may cause a propensity in the apparatus to overturn.
In Spencer, U.S. Pat. No. 5,306,103, a carriage assembly is disclosed which supports a trench box in a suspended relationship having a pair of axles, a pair of spaced apart bracket elements disposed on each axle, a pair of wheel assemblies disposed at opposite ends of each axle and a support member attached to each of the bracket elements in a downwardly depending relation thereto, the support member being connected to the trench box.
In Spencer, a support member extends for a portion of its length through a rigidifying member located near the outer edges of each of the two trench shields. The overall configuration of the Spencer apparatus results in a fairly rigid structure which may be suitable for lightweight panels, fabricated of aluminum for instance, and panels of a limited height and depth. However such a rigid configuration is unsuitable for use with large steel panels used in many applications. Once again, vertical travel of the trench box is limited by the elevation of the frame and axles.
What is needed is an improved movable trench shoring device, for use with large steel trench shoring boxes, which is capable of supporting boxes which may reinforce and support trench banks as deep as 25-30 feet with shoring panels as wide as 36 feet. What is also needed is a portable or moveable trench shoring device which also provides a support means for the shoring box which allows for adjustment of the height of the shoring box or panels relative to the frame so that the top edge of the panel shoring box or panels may be adjusted above the elevation of the frame, thereby providing increased flexibility in the working dimensions of the device so that it may accommodate a variety of ditch depths without having to interchange larger panels for shorter panels. Additionally, it would be advantageous to have a device for shoring trenches which is moveable or portable and which allows for variation of the wheel base width. Additional objects, advantages and novel features of the invention will be set forth as part of the description that follows and, in part, will become apparent to those skilled in the art upon examination of the following or may be learned by practice of the invention.